Data update

Task/Queue-Definition/Ada/queue-definition-2.adb

@@ -0,0 +1,49 @@
+with Ada.Unchecked_Deallocation;
+
+package body Fifo is
+
+   ----------
+   -- Push --
+   ----------
+
+   procedure Push (List : in out Fifo_Type; Item : in Element_Type) is
+      Temp : Fifo_Ptr := new Fifo_Element'(Item, null);
+   begin
+      if List.Tail = null then
+         List.Tail := Temp;
+      end if;
+      if List.Head /= null then
+        List.Head.Next := Temp;
+      end if;
+      List.Head := Temp;
+   end Push;
+
+   ---------
+   -- Pop --
+   ---------
+
+   procedure Pop (List : in out Fifo_Type; Item : out Element_Type) is
+      procedure Free is new Ada.Unchecked_Deallocation(Fifo_Element, Fifo_Ptr);
+      Temp : Fifo_Ptr := List.Tail;
+   begin
+      if List.Head = null then
+         raise Empty_Error;
+      end if;
+      Item := List.Tail.Value;
+      List.Tail := List.Tail.Next;
+      if List.Tail = null then
+         List.Head := null;
+      end if;
+      Free(Temp);
+   end Pop;
+
+   --------------
+   -- Is_Empty --
+   --------------
+
+   function Is_Empty (List : Fifo_Type) return Boolean is
+   begin
+      return List.Head = null;
+   end Is_Empty;
+
+end Fifo;